In the paper industry, hooded drying cylinders, i.e. Yankee dryers, etc. are standard equipment for making a variety of paper products such as tissues and paper towels. A dryer generally consists of a large, rotating cylinder which is internally heated with steam. A major portion of the surface of the cylinder is encompassed by a hood which is continuously provided with hot air for drying the sheet and exhausting moisture. The wet paper web to be dried is briefly adhered to the outer surface of the rotating cylinder on a continuous basis. In the short time the web is in contact with the rotating cylinder, most of the moisture is driven out of the web by a combination of the dryer surface heat and the hot air. The moisture is carried away by the hot air circulating through the hood.
A difficulty with such drying systems is that large quantities of energy are required to provide the steam for the drying cylinder and hot air for the dryer hood. The steam is generally supplied from a boiler house, often remotely located, which is a major capital expenditure and costly to operate. Hot air for the dryer hood is generally supplied by the combustion of natural gas or light oil in a direct fired burner or by steam coils.
Therefore, because of the high costs of energy as a percent of manufacturing cost, there is a need for a more economical method of providing hot air and steam to such dryers.